In a mobile communications system, to guarantee the service quality of wireless communications, a communications network and communications equipment have strict requirements for clock synchronization; and in particular, with the development of the third generation mobile communications technology in the mobile communications network, the mobile communications system has more strict requirements for the precision of clock synchronization.
The IEEE 1588 V2 protocol is a protocol of frequency and time synchronization, the full name of the IEEE 1588 V2 protocol is the Precision Clock Synchronization Protocol for Networked Measurement and Control Systems, or the PTP protocol for short. The IEEE 1588 V2 protocol is a universal standard for improving timing synchronization capability of network systems, provides strict timing synchronization for distributed communications networks and is applied in industrial automation systems. By adopting the 1588 V2 protocol, the precision may reach a sub-microsecond level. FIG. 1 shows a main principle of time synchronization of the protocol, of which a basic idea is to synchronize an internal clock of a piece of network equipment (a client) and a master clock of a master controller through hardware and software, and provide an application of which synchronization establishing time is less than 1 μs, so as to remarkably improve the timing synchronization index of an entire network.
Generally, for communications nodes in the mobile communications system, each node needs at least two fiber links to reach a neighboring node: one is a receiving link and the other is a sending link. A basis for implementing precise time synchronization between nodes through the 1588 protocol is that the receiving and sending fiber links of a node need have equal lengths. If the lengths of the receiving and sending fiber links are not equal, asymmetric compensation should be performed for the fibers, otherwise the inconsistency between the receiving and sending fiber links may have serious impacts on the precision of time synchronization. In this case, asymmetry between the receiving fiber link and the sending fiber link needs to be measured.
In a current solution, the GPS is used to perform node-by-node measurement and compensate the fibers with an asymmetric value. As shown in FIG. 2, the asymmetry of fibers between nodes NE1 to NE4 is measured node by node, and the asymmetric value is compensated with according to a measurement result. The prior art has three defects: nodes NE1 to NE4 all need to be measured on site, which leads to a heavy workload; the GPS should guarantee that a satellite is in the visual range of a receiver, and when a base station is placed in a site which is not suitable for deploying a GPS antenna, such as a basement or a metro station, it is difficult to carry out on-site measurement; and the most important point is that a fiber may change after the fiber is disconnected in a node and the measurement needs to be performed again on site.
For the foregoing measurement of the fibers and asymmetric value compensation for the fibers, it is found that this method has the following problems: every node needs to be measured on site, which leads to a heavy work load, and the measurement needs to be performed again on site when a fiber is disconnected in a node. Therefore, the operability of the prior art is rather poor.